1. Field of the Invention
The present invention relates to a clutch assembly structure for a multiple disk clutch used in a power transmission system of an automobile.
2. Description of the Prior Art
A multiple disk clutch has been widely used in a power transmission system of a motor vehicle such as an automobile. Examples of conventional multiple disk clutches are disclosed in Japanese Patent Application Laid-open No.s 63-246544 and 2-3706 for example.
Referring to FIG. 4, the multiple disk clutch disclosed in Japanese Patent Application Laid-open No.63-24655 has a first clutch assembly a and a second clutch assembly b which are coaxially arranged in parallel with each other such that the first clutch assembly a is disposed radially outwardly of the second clutch assembly b. The first clutch assembly a includes a drum c1, clutch disks or plates d1 accommodated in the drum c1, a first piston e1 adapted to press the clutch disks d1 for engagement thereof and a return spring f1 serving to bias the first piston e1 backward i.e. away from the clutch disks d1. Similarly the second clutch assembly b includes a drum c2, clutch disks b2, a second piston e2 and a return spring f2. Both of the first and second clutch assemblies a, b employ coil springs for the return spring f1, f2.
Referring to FIG. 3, the multiple disk clutch disclosed in Japanese Patent Application Laid-open No.2-3706 has a first clutch assembly h and a second clutch assembly i which are coaxially arranged in parallel with each other such that the first clutch assembly h is disposed radially outwardly of the second clutch assembly i. The second piston j2 has a smaller effective diameter than the first piston j1 and is received inside a sliding surface between the first and second pistons j1, j2 so as to reduce the axial distance between the first and second pistons j1, j2. Return spring k is provided for biasing the first piston j1 backward, and the second piston j2 serves to receive or withstand a reaction force from the return spring k.
In the multiple disk clutch disclosed in Japanese Patent Application Laid-open No.63-246544 the use of coil springs for the return springs f1, f2 of both of the first and second clutch assemblies a, b increases axial dimensions of these clutch assemblies a, b resulting in an undesirably large overall size of the clutch.
In the multiple disk clutch disclosed in Japanese Patent Application Laid-open No.2-3706 an oil chamber m containing the second piston j2 and serving to cancel a centrifugal oil pressure which biases the first piston forward has a relatively large volume, and it takes a relatively long time to fill the chamber m with oil. Consequently the centrifugal oil pressure in the oil chamber m is not sufficiently applied to the second piston j2 which as a result does not satisfactorily function to cancel the biasing centrifugal oil pressure.
Further, the second piston j2 as described above and the return spring k consisting of a coil spring are interposed between a hub side wall p supporting clutch disks n and the first piston j1 adapted to press the clutch disks n. In this arrangement, the clutch assembly tends to have a relatively large axial length or dimension resulting in an undesirably increased overall size of the clutch.